Hot Tub Wiring Explained: Spa Pack Wiring, Cable Sizes and RCD/GFCI (UK and US)

Last updated: September 2026

In this post I’m explaining hot tub wiring: how the supply gets to your spa pack, and how the pumps, blower and other bits connect to it. If you want the bigger picture on your electrical supply, such as how much current you need and why 240V matters, read my guide to hot tub electrics alongside this one.

Let me be clear up front. I’m a DIY builder and I’ve done electrics before, but the final connection of your hot tub supply must be done by a qualified electrician. What I can do is help you understand what’s going on, so you can plan the control room, buy the right parts and talk to your electrician on the same page.

Who does what: DIY vs electrician

On a DIY build, the split usually looks like this:

• You can plan the control room, mount the spa pack, fit the pumps and blower, and plug them into the pack using the manufacturer’s plugs or terminals. Always do this with the power isolated and locked off.
• Your electrician designs and installs the supply, from the consumer unit or panel, through the cable run and isolator or disconnect, to the pack’s terminal block. They also test it and certify it.

In the UK, a new hot tub circuit is notifiable work under Part P of the Building Regulations. The Planning Portal says the electrics need to be installed “by a registered competent person”. That means an electrician who can self-certify and give you an Electrical Installation Certificate. In the USA, most areas need a permit and inspection for a hot tub circuit, following NEC Article 680 as adopted locally. My post Do I need a permit for my hot tub? covers that.

The big picture: from supply to pumps

Before we get into the detail, here’s how it all fits together.

The spa pack is the central control

The spa pack is the brain of your hot tub. It controls the temperature, and it controls the pumps and blower. Packs look different from one manufacturer to the next, but the job is the same: control all the electrical parts in your hot tub.

In its most basic form, a spa pack is a set of fancy relays. When you want heat, a relay closes and sends power to the heating element. When you want the jets, a relay closes and sends power to your pump. That’s why the mains supply goes directly to the pack, and the pack distributes it to everything else. You don’t wire the pumps to their own supplies.

The supply: UK vs USA

This is where the two sides of the Atlantic differ most.

	UK and Europe	USA
Voltage	230V single phase, 50Hz (three phase on some bigger setups)	240V split phase, 60Hz: two hot legs (L1, L2), a neutral and a ground
Typical DIY pack rating	Balboa BP packs are set up for 16A or 32A, with a maximum 20A or 40A breaker	Around 40–50A. The ACC SmartTouch 1000 I use is rated 240V, 41A
Shock protection	30mA RCD, Type A as a minimum (or the type the maker specifies), usually as an RCBO	GFCI protection (NEC 680), usually a GFCI breaker in a spa disconnect
Local isolation	Rotary isolator within sight, typically at least 2m from the water	Maintenance disconnect within sight, at least 5ft (1.5m) horizontally from the inside wall
Outdoor cable	Steel wire armoured (SWA), or cable in suitable ducting	Copper conductors (e.g. THHN) in conduit. Never aluminium
Mains wire colours	Brown = line, blue = neutral, green/yellow = earth	Black and red = hot legs, white = neutral, green = ground
Paperwork	Part P notification and an Electrical Installation Certificate	Permit and inspection in most areas

What about 110V or 120V in the USA?

If you’ve built a tub from block or concrete, 120V won’t do it. A 15A circuit at 120V can only supply about 1.8kW in total, for everything. Plug-and-play tubs get around this by not running the heater and jets at the same time, as Bullfrog Spas explains. A DIY in-ground tub holds far too much water for that. Use a 240V supply. The good news is that almost every American home already has 240V coming in, for things like the dryer and the range.

Cable size

There’s no single cable size for a spa pack, and UK and US figures differ:

• UK: most DIY builds with a Balboa pack run on a 32A circuit (Balboa’s BP601 tech sheet gives 16A or 32A service, on a 20A or 40A maximum breaker). Total Skills’ guide gives 6mm² for a typical 32A run and 10mm² for 40A, with SWA outdoors. But voltage drop must stay within 5%, so a long run to the bottom of the garden often needs a bigger cable. If your setup needs more current, for example a separate heat pump, that changes things again.
• USA: ACC specifies #6 AWG copper conductors for its 41A SmartTouch 1000 pack. A 50A spa circuit is usually wired in #6 AWG copper, as ExpertCE’s hot tub wiring guide notes. Longer runs may need bigger wire.

The rule is simple. Take the pack’s rating from its label or tech sheet, add anything else on the same circuit, and let your electrician size the breaker and cable for the load, run length, installation method and voltage drop. My hot tub electrics guide shows how to add up the current.

Burying the cable

• UK: Total Skills gives a minimum burial depth of 500mm (20in) for SWA in a garden, or 600mm (24in) under areas with vehicle access. Lay warning tape above it.
• USA: burial depth depends on the wiring method (NEC Table 300.5). Hot Tub Outpost gives 18in (450mm) for PVC conduit and 6in for rigid metal conduit. Check with your inspector.

Either way, plan the route before you pour any concrete, and put a duct or sleeve under slabs and paths. It’s covered in my groundwork guide.

RCD and GFCI protection

This is the bit that keeps you alive. A hot tub puts wet, barefoot people next to 230V or 240V, so it gets extra protection.

• UK: a 30mA RCD is a must, and it needs to be at least Type A, because hot tub electronics can produce leakage a basic Type AC RCD may not detect. Follow the pack or tub manufacturer if they specify a type. An RCBO for the hot tub circuit in your consumer unit is the neatest way to do it, and it means a tub fault doesn’t take your house circuits down.
• USA: NEC Article 680 requires GFCI protection for a hot tub. It usually comes from a GFCI breaker in a spa disconnect panel (a “spa panel”) near the tub, or from a GFCI breaker in the main panel.

The IET’s guidance on outdoor hot tubs recommends applying BS 7671 Section 702 (swimming pools) in full. That covers zones around the water, IP ratings, fixed wiring and whether PME earthing is suitable. That last point is one for your electrician. It’s a good reason not to treat a hot tub like any other garden socket.

If your RCD or GFCI trips, don’t just keep resetting it. It’s telling you something. Work through my breaker tripping troubleshooting guide.

The local isolator or disconnect

You need a way to switch the tub off that you can see from where you’re working. In the UK that’s a weatherproof rotary isolator (IP65 is typical) rated for the circuit, about 2m from the water’s edge so it can’t be reached from the tub. Total Skills and NAPIT both give 2m. In the USA it’s a maintenance disconnect within sight, at least 5ft (1.5m) horizontally from the inside wall of the tub (NEC 680.13). This is usually the GFCI spa panel. Where your control room sits drives all of this, so read The importance of control room position before you fix anything to a wall.

The spa pack terminal block

Depending on your pack, the main terminal block looks a little different. Below are two examples. The first is my favourite pack for US builds, the ACC SmartTouch 1000. The second is a Balboa.

On a UK Balboa pack on a single-phase supply, the terminal block takes line, neutral and earth. On a US 240V pack, you’ll have L1, L2, neutral and ground. That’s the 4-wire supply. The neutral is there for the 120V parts inside the pack, such as the ozonator. The wiring diagram inside the lid shows exactly where each goes, and any jumpers to change for your supply. Demystifying spa pack wiring diagrams walks you through reading one.

Connecting the pumps

Some pumps come with a cable already fitted and others don’t. It depends on the brand. Either way, hot tub pumps fall into two types.

Circulation pumps vs jet pumps

A circulation pump moves water through the heater and filter at low speed, drawing very little current. Circ pumps are usually single speed, and smaller and quieter than jet pumps. Jet pumps can be single or dual speed. They’re much bigger and push a lot more water through the jets. How many pumps do you need? helps you decide on the mix.

Single speed vs dual speed pumps

For wiring, what matters is this: a single-speed pump has a 3-core cable, and a dual-speed pump has a 4-core cable. The extra core is the second speed. Get high and low speed the wrong way round and you’ll have problems.

3-core cable (single-speed pump)

4-core cable (dual-speed pump)

Here are typical colour codes for US and European pump cables. Colours vary, so treat these as examples only.

Match the pin-out, not the colours

I can’t stress this enough. Don’t wire a pump by matching colours. Manufacturers change things all the time. Cords may not have the colours in the order you expect, and pumps change too. Follow the pin-out diagram for your pack, then trace each pin across to the right terminal on the pump: high speed, low speed, common and earth.

Different brands order their pins differently. Here’s the ACC pin-out, which shows which pin is high speed and which is low:

And here’s the Balboa pin-out, used on Balboa packs and the Balboa-made Vian Power:

You can clearly see the ACC and Balboa pin-outs are in a different order. A pump cord made up for one won’t be right for the other.

If a pump hums but won’t start once it’s wired, it’s often the capacitor, not your wiring. See The ultimate guide to hot tub pump capacitors.

Connecting a blower and other accessories

Accessories like a blower usually connect with a 3-core cable and use one output voltage. Which pins they use differs from pack to pack. On the ACC pin-out above, the blower pins are completely different from a pump’s. On a UK/EU Balboa pack, a blower generally uses line, neutral and earth. Check the diagram for your pack. The good news is that if you get the pin-out wrong on an accessory, you’re unlikely to damage it. It just won’t work.

Lights are a different story. The pack’s light output is low voltage and designed for its own lights. Don’t assume you can plug any pool light into it. I’ve covered this in Can I control a swimming pool light with a hot tub spa pack?

Configuring the pack after wiring

Once everything’s connected, the pack needs to know what you’ve plugged in. If it doesn’t, the buttons won’t do what you expect, and it’s easy to think the wiring’s wrong. I’ve written full guides to configuring a Balboa spa pack and programming a BP8 with a TP700, so here’s the short version.

1. Pick the setup number

On the underside of a Balboa pack’s lid, you’ll find a circuit diagram like this one:

Find the setup table and pick the number that matches your equipment. Check carefully: on this 18-setup table (the same one the Vian Power and BP8 use), #12 is a 2-speed pump and blower with a circulation pump. Without a circ pump, it’s #17. Other packs number their setups differently, so always read your own lid.

2. Set it on the topside

On the Balboa TP-series topsides I was using, the low-level setup menu was reached like this. Check your topside’s manual, as the button names and sequence vary:

1. Turn the tub off.
2. Move DIP switch 1 to ON.
3. Turn the tub on.
4. On the topside, press “WARM” twice, then “LIGHT”, then “WARM”.
5. Use “WARM” to scroll to the setup number you need.
6. Press “LIGHT” to save.
7. Turn the tub off, move DIP switch 1 back to OFF, and turn it on again.

3. Set the DIP switches for your supply

Most Balboa packs have a bank of DIP switches. In short, they tell the pack how many high-speed devices (pumps or blower) can run with the heater before it switches the heater off, so the pack stays within your supply. Check the diagram in your own lid, because the order can differ. On the packs I’ve used:

• A1: test mode (normally off).
• A2, A3, A4: add one, two or four high-speed devices that can run with the heater. They combine, so A2 and A3 on allows three. All off means no heat with any high-speed pump or blower running.
• A5: Special Amperage Rule A (off, no limitation) or B (on, limits how many high-speed pumps can run).
• A6: persistent memory reset on power-up.
• A7: heater cool-down time. 1 minute for electric heaters (off), or 5 minutes (on) for some gas heaters.

Don’t guess. I used to tell people to set everything to “no limitation” if they weren’t sure and let the electrics trip, but I wouldn’t do that now. The breaker is there to protect the cable, not to be your load control. Set the DIP switches to match the supply your electrician has installed. On a 16A UK supply, that means letting the pack switch the heater off while the jets run. Balboa’s BP tech sheets list the switch settings for each service type.

ACC SmartTouch 1000: quick wiring reference (USA)

I use the ACC SmartTouch 1000 on a lot of US builds, and it’s still available at parts4tubs.com. From the ACC SmartTouch 1000 guidelines:

• The system is 240V, 41A at 60Hz, fed with #6 AWG copper conductors on a 4-wire supply. It can be set up for 120V, but I don’t supply parts for 120V, as it’s underpowered for a DIY tub.
• Supply terminals: neutral in the middle, Line 1 on the left, Line 2 on the right.
• For 240V, move the blue wire (pump) and the red and white striped wire (blower) from the neutral terminal to Line 2. The solid white wire stays where it is.
• On the supplied pump cords: black is high speed, red is low speed, white goes to white on the pump and green goes to green.
• The blower plugs into “Air Blower”, and the pump into “Primary Pump”. Check your pump’s own diagram for its high and low terminals.
• Don’t connect the pool light I supply to the ACC control unit. It isn’t compatible.

If an ACC pack throws PSOL or PSOH errors after wiring, that’s the pressure switch, not the mains wiring. See ACC spa controller PSOL and PSOH errors.

Common wiring mistakes

• Wiring pumps by colour instead of the pin-out, so high and low speed end up swapped.
• Leaving an ACC pack on its 120V jumpers on a 240V supply, or the other way round.
• Undersized cable on a long run. The pack browns out, the heater is slow, and connections run hot.
• Using a Type AC RCD, or sharing an RCD with house circuits, so the tub trips everything.
• Putting the isolator where it can be reached from the tub, or out of sight of it.
• Wrong setup number, so a button does nothing or runs the wrong pump.
• DIP switches set for more current than the supply, so the breaker trips when the heater and jets run together.
• No duct under the slab, which means digging up the patio later.

First power-up troubleshooting

• Nothing at all: check the isolator, breaker, RCD or GFCI, and any fuses on the pack’s board.
• RCD or GFCI trips instantly: suspect a wet connection, a damaged cord or a heater element fault. Isolate, then test each device one at a time. The breaker tripping guide goes through it.
• A pump runs on the wrong speed: high and low are swapped at the plug or pump terminals.
• The blower or a pump won’t come on: check the setup number and overlay before touching the wiring.
• No heat: check flow and the pressure or flow switch first. See Help! My hot tub is not heating.

Planning your own build?

Wiring is much easier when the control room is laid out properly from the start: space for the pack, the pumps, the isolator and a sensible cable route. The Ultimate Hot Tub Control Room Guide covers exactly that, and my DIY hot tub plans include the plumbing layout and a full parts list. There’s more on control room layout in Hot tub control room design considerations.

If your build is custom, I can draw it up as architectural CAD with a 3D plumbing design, which you can hand to your builder and electrician. Parts are available from parts4tubs.co.uk in the UK and parts4tubs.com in the USA.

FAQs

Can I wire my own hot tub?

You can mount the pack and plug in the pumps and blower yourself with the power isolated. The supply itself (circuit, cable, RCD or GFCI, isolator and connection at the pack) should be done by a qualified electrician. In England and Wales it’s notifiable under Part P, and in the USA it usually needs a permit.

What size cable do I need for a hot tub?

It depends on the pack’s current rating, the run length and how the cable is installed. As a guide, a 32A UK circuit is often 6mm², going up to 10mm² for 40A or long runs, in SWA outdoors. A US 50A spa circuit is usually #6 AWG copper. Your electrician confirms it with a voltage drop calculation.

What RCD do I need for a hot tub in the UK?

A 30mA RCD of at least Type A, or whatever type the manufacturer specifies, ideally as a dedicated RCBO for the hot tub circuit.

Does a hot tub need a GFCI in the USA?

Yes. NEC Article 680 requires GFCI protection for hot tubs. It’s usually provided by a GFCI breaker in a spa disconnect at least 5ft from the tub and within sight of it.

Can I run a DIY hot tub on 120V?

Not realistically. A 120V 15A circuit gives around 1.8kW in total, which isn’t enough to heat a block or concrete tub while the jets run. Use a 240V supply.

Why is my dual-speed pump running on the wrong speed?

The high- and low-speed wires are swapped. Check the pack’s pin-out and the pump’s terminal diagram rather than the wire colours.

Got a question about wiring your own tub? Drop it in the comments below. I read them all.

Cheers,
Andi

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Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi